The present invention relates to the area of zeolites. Zeolites may be natural or synthetic and are inorganic crystalline aluminosilicates, with a highly regular structure of pores and channels rendering them suitable for molecular sieving, adsorption, ion exchange, dehydration, and rehydration processes for example. They generally have a definite crystalline structure as evidenced by x-ray diffraction.
Zeolites have long been known to have catalytic properties for various types of hydrocarbon conversion processes.
There are around 40 types of natural zeolites and over 200 types of synthetic zeolites. However, there are less than 10 commercial zeolites. The cavities or voids within a zeolite are specific to that zeolite and uniform in size within that material. The active catalytic sites in the zeolite voids can only operate on molecules that can fit through the openings into the zeolite structure.
The lamellar zeolites, ie., zeolites with platelet morphology or sheath-like structures, are being scrutinized recently. The reason behind this search for lamellar structures is to obtain a material composite containing both micropores and mesopores separated by a gallery of pillars. These pillars might be porous crystalline network of different species such as, silica, alumina, MgO or organic surfactants such as C16-amine or non-porous network of silica. The result is the enhancement of surface area, reduction in the diffusion path and easy access to the active sites directly from the surface.
Only very few zeolites are known so far with lamellar/platelet morphology. U.S. Pat. No. 4,954,325 Rubin et al. describes MCM-22, a novel zeolite that is obtained by the calcination of a layered precursor.
Upon pillaring with silica or C16-amine, another new material, MCM-36, was obtained (U.S. Pat. No. 5,250,277). Upon delamination of the layers, the material obtained is a novel phase that contains sheets of MCM-22 zeolites, termed as ITQ-2 (A. Corma et al., Microporous and Mesoporous Mater., 2000, 38, 301).
A delaminated material, ITQ-6, was obtained from Ferrierite (P. A. Vaughan, Acta Crystallogr. 1966, 21, 983). A layered silicate composed of hydrogen bonded ferrierite layers, MCM-47, was reported by Burton et al. (Chem. Mater., 2000, 12, 2936) The zeolite ferrierite [FER] is structurally related to zeolite ZSM-57 (J. L. Schlenker, J. B. Higgins and E. W. Valyocsik, Zeolites, 1990, 10, 293). Recently, another lamellar zeolite, NU-6, was used to obtain a pillared material, and subsequent delamination resulted in a new phase ITQ-18 (U.S. Pat. No. 4,397,825; U.S. Pat. No. 5,266,541)
Zeolite ZSM-57 (U.S. Pat. No. 4,873,067) is a medium pore zeolite [10-MR] with interconnected 8 MRs. It is related to ferrierite type zeolite [FER]. The structure code for ZSM-57 is MFS. Few applications of this zeolite are known. The zeolite ZSM-57 was found to have platelet morphology with pentagonal crystals.